Root/mm/percpu-km.c

1/*
2 * mm/percpu-km.c - kernel memory based chunk allocation
3 *
4 * Copyright (C) 2010 SUSE Linux Products GmbH
5 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
6 *
7 * This file is released under the GPLv2.
8 *
9 * Chunks are allocated as a contiguous kernel memory using gfp
10 * allocation. This is to be used on nommu architectures.
11 *
12 * To use percpu-km,
13 *
14 * - define CONFIG_NEED_PER_CPU_KM from the arch Kconfig.
15 *
16 * - CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK must not be defined. It's
17 * not compatible with PER_CPU_KM. EMBED_FIRST_CHUNK should work
18 * fine.
19 *
20 * - NUMA is not supported. When setting up the first chunk,
21 * @cpu_distance_fn should be NULL or report all CPUs to be nearer
22 * than or at LOCAL_DISTANCE.
23 *
24 * - It's best if the chunk size is power of two multiple of
25 * PAGE_SIZE. Because each chunk is allocated as a contiguous
26 * kernel memory block using alloc_pages(), memory will be wasted if
27 * chunk size is not aligned. percpu-km code will whine about it.
28 */
29
30#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
31#error "contiguous percpu allocation is incompatible with paged first chunk"
32#endif
33
34#include <linux/log2.h>
35
36static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
37{
38    /* noop */
39    return 0;
40}
41
42static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size)
43{
44    /* nada */
45}
46
47static struct pcpu_chunk *pcpu_create_chunk(void)
48{
49    const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
50    struct pcpu_chunk *chunk;
51    struct page *pages;
52    int i;
53
54    chunk = pcpu_alloc_chunk();
55    if (!chunk)
56        return NULL;
57
58    pages = alloc_pages(GFP_KERNEL, order_base_2(nr_pages));
59    if (!pages) {
60        pcpu_free_chunk(chunk);
61        return NULL;
62    }
63
64    for (i = 0; i < nr_pages; i++)
65        pcpu_set_page_chunk(nth_page(pages, i), chunk);
66
67    chunk->data = pages;
68    chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
69    return chunk;
70}
71
72static void pcpu_destroy_chunk(struct pcpu_chunk *chunk)
73{
74    const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
75
76    if (chunk && chunk->data)
77        __free_pages(chunk->data, order_base_2(nr_pages));
78    pcpu_free_chunk(chunk);
79}
80
81static struct page *pcpu_addr_to_page(void *addr)
82{
83    return virt_to_page(addr);
84}
85
86static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai)
87{
88    size_t nr_pages, alloc_pages;
89
90    /* all units must be in a single group */
91    if (ai->nr_groups != 1) {
92        printk(KERN_CRIT "percpu: can't handle more than one groups\n");
93        return -EINVAL;
94    }
95
96    nr_pages = (ai->groups[0].nr_units * ai->unit_size) >> PAGE_SHIFT;
97    alloc_pages = roundup_pow_of_two(nr_pages);
98
99    if (alloc_pages > nr_pages)
100        printk(KERN_WARNING "percpu: wasting %zu pages per chunk\n",
101               alloc_pages - nr_pages);
102
103    return 0;
104}
105

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